Age-related changes in motor control during articulator visuomotor tracking.

The present study provides normative data on changes in visuomotor control of the oral-facial system across the lifespan. Control of the lower lip, jaw, and larynx (i.e., fundamental frequency) was examined using a nonspeech visuomotor tracking (VMT) task, where subjects move the articulator of interest to track a moving target on an oscilloscope screen. This task examines articulator motor control during movements that are similar to speech but that do not impose linguistic units or the demands of coordinating multiple structures. Accuracy and within- and between-subject variability in tracking performance were measured by cross correlation, gain ratio, phase shift, and target-tracker amplitude difference. Cross-correlation analyses indicated that performance of children (aged 8;2 to 17;0 [years;months]) and older adults (aged 45;1 to 84;3) is poorer than that of younger adults (aged 17;1 to 45;0). Accuracy of movement amplitude tended to increase during development and decline with aging, whereas age did not appear to influence accuracy of temporal parameters in lip and jaw tracking. In contrast, age tended to influence individual variability in temporal but not amplitude parameters. Differences were noted between articulators. The data complement previous studies that considered accuracy and variability of articulator movement during speech. The VMT method and the data provided may be applied to assessment of impairments in the motor speech system and to differential diagnosis of motor speech versus linguistically based disorders.

The effects of varying signal intensity on the perceptual organization of rhythmic auditory patterns.

Cyclic repetitions of temporally structured sequences of sound bursts and gaps are perceived as rhythmic patterns. Some are perceptually unambiguous--the pattern organization is unique; others are perceptually ambiguous--the organization changes. Previous research suggests that the pattern of neuronal adaptation and recovery from adaptation associated with these stimuli determines how listeners perceptually organize the sequences. It follows that variations in the intensity of specific sound elements, which should produce specific changes in the underlying patterns of neuronal activation, should produce predictable changes in the perceptual organization of the sequences. The present study tested this hypothesis by observing the perceptual responses of listeners while varying the intensity of critical elements of unambiguous and ambiguous sequences. The results support the hypothesis in that an unambiguous sequence was made ambiguous and an ambiguous sequence was made less ambiguous. However, the unambiguous sequence did not completely reverse its perceptual organization, nor did the ambiguous sequence become completely unambiguous. The outcome is discussed focusing on the range of intensity increments tested, the type of stimuli used, and the possibility that neurosensory factors may interact with other organizing factors in determining the perceptual organization of rhythmic auditory sequences.

Endogenous visuospatial precuing effects as a function of age and task demands.

This experiment examined the effects of age on processing resource capacity using an endogenous visuospatial precuing task and four levels of resource demands. Younger and older adults made speeded two-choice responses to dim and bright targets that required a line-orientation or a lexical decision. An arrow preceding target onset served as an attentional cue to affect the spatial distribution of resources. It provided accurate information about the target's location on most trials and inaccurate or neutral information on the remaining trials. Although older adults were slower than younger adults under all conditions and were more affected by the resource demand manipulations, they exhibited a pattern of precuing effects across conditions that was similar to that of the younger adults. Results are consistent with the idea that the visuospatial attention system remains relatively unaffected by aging. However, the data speak against the idea that capacity reduction is the primary contributor to age-related slowing.

Natural boundaries for the spatial spread of directed visual attention.

The spatial characteristics of directed attention were studied using spatial precues in a suprathreshold luminance detection task. Visual response times to probe flashes presented at various distances from the presumed focus of attention provided the dependent measure. The variation in response times with distance from the attentional focus was used to create spatial maps of the expectancy effect. The results indicate that, in an uncluttered visual field, the effects of precuing are widely distributed, and that the principal transitions in performance tend to occur either at the horizontal meridian, the vertical meridian, or both meridians, depending on the locus of the observers' expectancy.

Distractor-target interactions during directed visual attention.

The spatial extent of directed visual attention (DVA) was examined in a series of experiments using precuing in a suprathreshold luminance detection (reaction time) paradigm. Previous findings (Hughes, H. C. and Zimba, L. D. J. Exp. Psychol.; Human Percept Perf., 1985, 11, 409-430) indicated that, in an empty visual field, the effects of DVA were primarily manifest as a uniform elevation of response times to all probe targets in the hemifield contralateral to the observer's expectancy. The present experiments were designed to determine whether increased spatial selectivity could be found when luminous markers indicated the exact location of the expected visual target. To maintain equivalent states of adaptation in both hemifields, luminous markers were also present at the same location in the contralateral hemifield. In general, hemifield effects were again obtained, but with two notable exceptions. First, marking locations in the unattended hemifield produced a local increase (enhanced interference) in RTs above the level characteristic of other locations within that hemifield. Second, when multiple locations were indicated with identical luminous markers, graded costs were obtained in both hemifields. However, scaling the markers according to estimates of cortical magnification factor (M) substantially reduced the slope of these inhibitory gradients, and the results once again approached those characteristic of an unstructured visual field. The findings suggest that when attention is directed to a marked location along the horizontal meridian, a transition in performance typically occurs at the vertical meridian. In addition, irrelevant stimuli some distance from the attentional focus interfere with detection times to unexpected targets that appear in the same vicinity. This interference may relate to an enhanced susceptibility to spatial interactions between the distractors and target away from the attentional focus. The interference appears to extend over a constant area of visual cortex, since it is reduced when the markers are M-scaled.

Spatial maps of directed visual attention.

Simple reaction times (RTs) to a visual target are facilitated when the target occurs at a location expected by an observer, and are slowed when the target occurs at the mirror-symmetric location contralateral to the expectancy (e.g., Posner, 1978; Posner, Snyder, & Davidson, 1980). The spatial extent of this attention effect was examined by inducing subjects to expect the target at one location and introducing occasional probe flashes at other locations throughout the visual field. The results indicated that RTs to these probes were equivalent to those obtained at the expected location so long as the probe was in the same hemifield as the subject's expectancy. Conversely, RTs to probes in the hemifield opposite the expectancy generated uniformly slower response times. These results were obtained when the expected location varied in eccentricity from 2 degrees to 16 degrees along the horizontal meridian. In addition, when the expected and unexpected locations were within the same hemifield, no expectancy effects were observed. Under these conditions, the frequently used metaphor that directed visual attention operates like a spatially restricted "beam" appears inaccurate. The implications of these findings for current views of directed attention are considered.

Binocular rivalry and semantic processing: out of sight, out of mind.

Previous studies of binocular rivalry have shown that some aspects of a phenomenally suppressed stimulus remain available for visual analysis. The question remains, however, whether this analysis extends to the case of semantic information. This experiment examines that question using a semantic-priming paradigm in which prime words were briefly flashed to an eye during either dominance or suppression phases of binocular rivalry. Reaction times on a lexical-decision task were significantly shortened (the semantic-priming effect) only when prime words were presented to an eye during dominance; suppression acted to impair word recognition and to eliminate semantic priming. These results are inconsistent with certain cognitive models of binocular rivalry.